Hit and Blow Onchain: An on-chain code-breaking PvP game

Hit and Blow Onchain

Hit & Blow is a popular code-breaking PvP game (also known as Bulls and Cows). The problem is that the game needs a third party to prevent cheating or miscounting in mid-game. By utilizing Zero Knowledge proofs, the game can achieve the integrity of the game without relying on any third party and be enabled to be fully onchain.

Hit and Blow Onchain is a onchain version of the game.

Application Type


Proposal Overview

Hit and Blow Onchain has already been deployed on mainnet and is playable. But there is still room for improvement in the current version.

  • Too many transaciton confirmation processes. (about 10 times or more per 1 game)
  • Can not play multi games simultaneously. (When other players are playing the game you can only just watch it.)
  • Not PvP but Player vs Bot. (Currently when you start playing the game, the bot automaticaly starts to play the game as your opponent for the convenience of a test play.)
  • No time limit. (When the player or bot stops playing in the middle, the game gets stuck…)
  • No upgradability.

and others…

Except the first one, the solution is relatively straightforward. Just implement these features. For the first one, I think the best solution is a developing native mobile app with an in-app wallet.

Use Case

  • For learning ZKP:
    The rules is very simple but writing or understanding its circuit needs a basic knowledge of Circom and ZKP. It’s source code can be a good learning resource.

  • For fun!:
    The game has lots of fans around the world.

  • For showing off Harmony’s fast block finality and low gas fees:
    This onchain game won’t work without fast block finality and low gas fees.

Competitive Landscape

There are many non-blockchain Hit & Blow game apps on Google Play Store & App store but very few onchain casual games. I believe after arrival of the mobile era on blockchain, onchain casual games will come to be developed.

Proposal Ask

Hit and Blow Onchain will be established to be community-driven and self-funded by the DAO (to be created). To get this up and running, we will be requesting the $15k/year stable basic income to take care of initial development, welfare and operations costs.

This ask will be in line with the laid down milestones as detailed below

  1. launching a feature-complete product on our testnet
  2. forming a DAO with 5-out-of-9 multisig with our DAOs
  3. launching on our mainnet with audit
  4. attracting 1k daily active users (with launch video, full PR promotion)
  5. attracting 10k daily active users (with a detailed roadmap, governance process)

Road Map

Objective Date Status
Testnet launch April 24th Done
Beta Testing and Fixes June 30th Pending
Smart Contract Audit Jul 15th Pending
Mainnet Launch Jul 16th Pending
Native mobile app client undecided Pending

The contract is already deployed on mainnet but before audit I’ll fix problems mentioned in the Proposal Overview section.

External links



Demo video:

Demo site:


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There’s a lot of potential here. I’m totally confused on how to play the game. Wish you could create a tutorial. As for our limiting issues; it’s good you pointed them out. What’s your plan to reduce those issue in the future?


I agree with you!
I’ll make a tutorial.

I think it will be great to make this as a mobile game and integrate with an in-app wallet. That will smoothen the UX a lot.

That being said, I think the current stage of the project is good for approval of the launch grant. Voting yes as a zkDAO governor, and confirming that the first milestone has been reached.

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I created “How to play” modal!
The show modal button is on the left top corner of the page.
I hope it will help users to understand the rules.

Great game to demonstrate zkp, appreciate the well-documented codebase and loading messages in the UI. The circuits also serve as a good teaching tool at ZKU.
Approved and milestone 1 confirmed

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